The invention relates to a fuel tank with ventilation system, wherein the fuel tank has a filler pipe, a filler neck with refueling sensor and a liquid level sensor, and the ventilation system comprises an activated carbon filter which, on the one hand, is connected by a first line to a vapor space of the fuel tank and by a second line to the induction tract of an internal combustion engine, and, on the other hand, by a third line to the atmosphere, an electronic control unit being provided, which on the input side is connected to the refueling sensor and to the liquid level sensor and on the output side is connected to the controlled valves, in such a way that the first and the third line, and also the second and the third line, can be mutually connected. The third line is separated from the first and second by the filter mass of the activated carbon filter. The vapor space is naturally in the upper part of the fuel tank.
Such fuel tanks with ventilation system are today firmly established within automobile construction for reasons of environmental protection. The ventilation systems fulfill a number of functions: they conduct the fuel-vapor-containing air, which has been compressed in the refueling operation and formed by evaporation, to the activated carbon filter, they conduct induction air through the activated carbon filter, for scavenging thereof, into the induction tract of the internal combustion engine (generally with the aid of a simple valve), cause the fuel nozzle to cut out as a result of the increase in pressure when maximum filling is reached, and prevent liquid fuel from escaping as a result of inertia forces or if the vehicle should overturn. For this purpose, float valves, nonreturn valves and rollover valves, all of them passive valves, are known. The various components of a ventilation system, as, too, those of the fuel supply system as a whole, are usually disposed at different places on or around the fuel tank and are connected to the latter by lines.
From U.S. Pat. No. 4,919,103, an installation of the generic type is known in which, in addition to the fuel pump, an activated carbon filter is also fitted inside the fuel tank. The line connections to and from the activated carbon filter are fitted, however, on the outside, and merely provided with simple nonreturn valves. A valve is seated on the filler neck and is mechanically opened upon introduction of the fuel nozzle and thus opens up a special line from the vapor space of the fuel tank to the activated carbon filter. A drawback with this installation is that the activated carbon filter is scavenged in an uncontrolled manner during normal running of the engine, in which case vapors can also be sucked up from the fuel tank. The emission limits which are currently in force can thus no longer be met, future ones still less.
From US 2001/0025668 A1, an installation according to the preamble of the 1st. claim is known, the valves of which are individually disposed at various places outside the fuel tank. In this particular installation, the activated carbon filter is fitted outside the tank. Consequently, the cost of pipework and command system, as well as the spatial requirement, is considerable. From U.S. Pat. No. 6,273,070 B1, it is known to equip an activated carbon filter with compartments for receiving various devices, including, inter alia, a so-called “rollover valve”, and to accommodate said filter inside a fuel tank.
The object of the invention consists in equipping a fuel tank with as simple and compact a ventilation system as possible, which fulfills all functions in full measure.